The desirability of generating swirling motion to an induction charge about the axis of an engine cylinder within a combustion chamber is well known. Such swirling motion produces a number of advantages in both the charge preparation within the combustion chamber and in the combustion of this charge within the combustion chamber. For example, in a conventional spark-ignition homogeneous engine operation, increasing swirl rate (usually defined as the ratio of in-cylinder charge rotative speed to engine rotative speed) has generally increased the burning rate and resulted in decreased fuel consumption. In stratified charge engines, some amount of swirl is also employed to promote mixing between the rich core of fuel and the surrounding air in order to reduce exhaust emission and fuel consumption. High swirl rates may also be beneficial to maintaining a centrally located fuel-air cloud in certain types of stratified charge engines. Swirl is also used in diesel engines to promote fuel-air mixing for lower NO.sub.x emissions and soot formation.
Various structural arrangements have been proposed to induce such directional admission of an induction charge into the combustion chamber of an engine. The use of a spiral or sloped intake passage; the use of a baffle or shroud in or adjacent the inlet port; and, the use of a baffle or deflector on the intake valve are well known examples of such structural arrangements. While such prior art structures have been effective in producing moderate amounts of swirl, they are limited in performance with swirl numbers usually on the order of 3 to 4, with reference to the definition of swirl rate as given hereinabove.